My Nikon kit looks like this... FE2 (just sold my F3), FG with a Tokina 17 3.5, 20 3.5, 24 2.8, 28 2.8 AI, 35mm 2.0 (AF-D), 50mm 1.4 AI, 60mm Micro (AF-D), 105 2.5 (P type), Vivitar S1 70-210 3.5
My OM kit looks like this... OM2n (three), OM4 with a Soligor 24 2.8 (mediocre), Kiron 28 2.0 (excellent) 2 50 1.8s, 50 1.4, 105 2.8, 75-150 4, Soligor 70-210 4 (above average)
I almost without hesitation use an OM over a Nikon (unless I have a specific lens in mind) mostly because of mechanics and ergonomics as mentioned above. I prefer the size and simplicity of the OM system lenses. As far as image quality goes, there's some differences in the equivalents that I own. In particular, the Nikon 105 is a lot better then the Zuiko 100. A lot. It also weighs twice as much. The 50 1.4s seem similar to me on the other hand. In general, I feel like my Zuiko lenses sorta "disappear" from the final images whereas the Nikons have a bit of "character" about them. That isn't meant to be a positive or negative, just a simple observation. The off brand stuff, well that's kinda irrelevant to any comparison. Frankly, if I want to use a system where the lenses really have character, I use my Spotmatic and associated Takumars.